JPS61133349A - Variable spectral reflectance alloy and recording material - Google Patents

Abstract

PURPOSE:To offer the titled alloy capable of holding spectral reflectances differ ent partially at the same temp., by compsing said alloy of Ag as main constitu ent, and specified compsn. quantities of Zn, groups Ia, IIa, IVa-VIIa, VIII, Ib-Vb and rare earth element, etc. CONSTITUTION:The titled alloy is composed of alloy contg. Ag as main compo nent, 30-46wt% Zn, <=15% total of >=one kind among groups Ia, IIa, IVa, Va, VIa, VIIa, VIII, Ib-Vb. rare earth element. on a part of surface of alloy having different crystal structures at the first temp. higher than room temp. and the lower second temp. than the first temp. in solid state higher than room temp., crystal structure different from that at said second temp. is formed by rapid cooling from said first temp.. By this way, different spectral reflectances are provided to said rapidly cooled part and unrapidly cooled part, to obtain the titled alloy.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a novel alloy with variable spectral reflectance and a recording material, and in particular to a novel alloy with variable spectral reflectance and a recording material, and in particular, the spectral reflectance of the alloy changes as the crystal structure of the alloy changes due to the application of light and thermal energy. This invention relates to alloys that can be used as media for information recording, display, sensors, etc. that utilize change.

[Background of the invention]

In recent years, as the density of information recording has increased and digitalization has progressed, various information recording and reproducing methods have been developed. In particular, optical disks that use laser light energy to record, erase, and reproduce information are capable of higher recording densities than magnetic disks, as stated in Industrial Rare Metals & 80.1983 (Optical Disks and Materials), and are expected to become more promising in the future. It is a powerful method of recording information. Among these, laser playback devices have been put into practical use as compact discs (CDs). On the other hand, recordable methods can be broadly divided into two types: write-once type and rewritable type. The former allows writing only once and cannot be erased, while the latter allows repeated recording and erasing.

In the write-once type recording method, a laser beam is used to destroy or shape the recording portion of the medium to create unevenness, and for reproduction, a change in the amount of light reflected due to the interference of the laser beam at the uneven portion is used for reproduction.

For this recording medium, it is generally known that Te or its alloy is used to form irregularities by melting and sublimating Te. This type of medium has some problems such as toxicity. Magneto-optical materials are the mainstream for rewritable recording media.

This method utilizes optical energy to invert and record the local magnetic anisotropy of the medium near the Curie point or compensation point temperature, and the polarization plane of the polarized incident light at that part due to the magnetic Faraday effect and magnetic Kerr effect. Play with the amount of rotation.

This method is considered to be the most promising rewritable method, and active research and development is underway with the aim of putting it into practical use in the next few years. However, at present, there is no material with a large amount of rotation of the plane of polarization, and even with various efforts such as multilayer film formation, the S/N and C/N
A major problem is that the output level is low. Other rewritable systems utilize changes in reflectance due to reversible phase changes between amorphous and crystalline recording media.For example, National Technical R
There is an alloy in which small amounts of Ge and Sn are added to TeOx described in eport Vo129 Ha 5 (1983).

However, this method reduces the crystallization part of the amorphous phase.

The instability of the phase at room temperature is a major problem that affects the reliability of the disk.

On the other hand, as an alloy utilizing color tone change, JP-A-57-1
There are 40845. This alloy is (12-15)wt%A
This is an alloy consisting of (1 to 5) wt% Ni and residual Cu, which takes advantage of the fact that it changes reversibly from red to gold at the martensitic transformation temperature. Since martensitic transformation is a transformation that inevitably occurs as the temperature decreases, the color tone obtained when the temperature is maintained above the martensitic transformation temperature cannot be brought below the martensitic modulation temperature. Conversely, if a color tone obtained at a temperature below the martensitic transformation temperature is lowered below the martensitic transformation temperature, a transformation occurs and changes to a different color tone.
Two color tones cannot be obtained at the same time at the same temperature, so this principle cannot be applied as a recording material.

[Purpose of the invention]

An object of the present invention is to provide a variable spectral reflectance alloy and a recording material that can maintain partially different spectral reflectances at the same temperature.

[Summary of the invention]

(Summary of the Invention) The present invention has silver (Ag) as the main component and zinc (Zo
) 30-46% and Ia, IIa, ■a.

The variable spectral reflectance alloy is characterized by comprising an alloy containing a total of 15% or less of one or more of Va, (1)a, (2)a, (2), tb-vb, and rare earth elements.

That is, the present invention provides a first temperature higher than room temperature (
In an alloy that has different crystal structures at a temperature (high temperature) and a temperature lower than the first temperature (low temperature), the alloy has a crystal structure that is different from that obtained by quenching from the high temperature than that obtained by non-quenching at the low temperature. It is a characteristically variable spectral reflectance alloy.

The alloy of the present invention is heated and cooled in a solid state.

It has at least two types of spectral reflectance at the same temperature and can reversibly change the spectral reflectance. In other words, the alloy according to the present invention has phases with different crystal structures in at least two temperature ranges in a solid state, and among these, the high temperature phase is quenched and the low temperature relaxation state is a standard state without quenching. The spectral reflectance is different, and the spectral reflectance changes reversibly by heating and cooling in the high temperature phase region and heating and cooling in the low phase temperature region.

The principle of reversible change in reflectance of the alloy of the present invention will be explained with reference to FIG. FIG. 1 shows an equilibrium phase diagram of a binary Ag-Zn alloy.

The principle of recording and erasing nine characters, nine figures, etc. as information will be explained with reference to FIG. 2, taking as an example the alloy having the composition [1] in FIG. This alloy is in the ζ phase at equilibrium. The color of this phase is silvery white, and a curve corresponding to the 1-spectral reflectance is obtained. When this alloy is heated to the stable temperature region (T4) of the β phase, which is a high temperature phase, and then rapidly cooled, the β phase cools appropriately.
Moreover, it becomes a β' phase with a regular crystal structure. The color tone of the alloy in this properly cooled state is pink, and the spectral reflectance is also ζ
It is very different from the phase state. When this alloy is heated in the ζ phase stable temperature range (below Te) (T3), β' transforms into the ζ phase, and the color tone of the alloy changes reversibly from pink to silvery white, and the spectral reflectance also changes to its original state. Return to Afterwards, this process can be repeated to record, reproduce, and record information with 0 or more color tone changes.
The material applied to the erasure is the crux of the invention. That is,
It can be used as a recording medium that takes advantage of changes in reflectance and color tone due to phase transition between different crystal phases.

Regeneration is at T□ humidity temperature, generally at room temperature.

At T1, energy is selectively applied to the silver-white material in the ζ phase, heated to T4, and then rapidly cooled. Then, that part becomes β' phase and changes color to pink. This corresponds to a record. The recorded portion can be reproduced by comparing this portion with other portions. By applying a different density of energy to this pink colored portion and heating and cooling it to T3, the phase transforms from β' to ζ and returns to silvery white. This corresponds to erasing the record. The above-mentioned recording, reproducing and erasing processes can also be performed by completely opposite color tone changes. That is,
By utilizing the β' → ζ transformation in the pink color of the β' phase, the yellow color that is recorded as silvery white is distinguished from the pink color and reproduced. Furthermore, it can be eliminated by changing the ζ phase to the β' phase.

Generally, electromagnetic waves are suitable as the above-mentioned energy. Specifically, various laser beams, electron beams, etc. are also suitable. For reproduction, light of any wavelength that shows a difference in spectral reflectance may be used.

That is, lasers, lamps, etc. in the ultraviolet to infrared region are suitable. Furthermore, since it can be recognized as a change in one color, it can also be used as a display element.

(Alloy Composition) The alloy of the present invention must have different crystal structures at high and low temperatures, and the rapidly cooled crystal structure must be formed by rapid cooling from the high temperature β phase; The phase formed by this rapid cooling must be able to change to the crystalline structure at a low temperature by heating at a predetermined temperature. Therefore, the Zn content is 30 to 46% by weight, and I a at II a + I 'V a @V
The total amount of one or more of a, Ib to vb, and rare earth elements is 15% by weight or less. Specifically, group Ia is Li, group IIa is Mg, (:,
B, ■A group is Ti and Zr.

Hf, Va group is V, Nbl Ta, Via group is Cr.

Mo, W, ■a group is M n , ■ group is Co, Rh, Ir
, Fe, Ru, OB, N, i, Pd, Pt, Ib group is Cu, Aq, IIb group is Cd, mb group is B.

AQ, Ga, In, IVb group is c, si, Ge9Sn,
Pd, Vb group is P, Sb, Bi, rare earth elements are Y, La
, Ce, Sm, Gd, Tb*D)'+Lu is preferable, particularly preferably 0.1 to 5%, these elements are β
' to the ζ phase (T2) is lowered. This has the effect of lowering the heating temperature when erasing recorded information.

(Non-bulk production method thereof) In order to obtain reflectance variability, the alloy of the present invention must be able to form a supercooled phase by heating and rapidly cooling the material. In order to create and store information at high speed, it is desirable to use a non-bulk material with a high rapid heating and cooling effect and a small heat capacity.In other words, the energy applied to a desired minute area allows the depth of only the desired area to be reduced. It is desirable to have a non-bulk material that has a volume that can change to a crystal structure different from the standard crystal structure throughout.Therefore, in order to produce high-density information in a desired micro area, non-bulk foils and films with small heat capacities are required. , thin wire or powder is preferable, and the recording density is 0.01 to 0.2 μm for producing information in a minute area with a recording density of 20 megapits/d or more.
Generally, intermetallic compounds are difficult to plastically work.

Therefore, it is effective to directly rapidly cool and solidify the material from the gas phase or liquid phase to form it into a predetermined shape as a method for producing foil, film, thin wire, or powder. These methods include the PVD method (vapor deposition, sputtering method, etc.), the CVD method, and the use of a member with high thermal conductivity that rotates the molten metal at high speed. In particular, molten metal quenching method in which molten metal is poured onto the circumferential surface of a metal roll and rapidly solidified.
electroplating.

There are chemical plating methods, etc. When using a film or powder material, it is effective to form it directly on the substrate or to apply it and adhere it to the substrate. When coating, it is best to use a binder that does not cause a reaction even when the powder is heated.Also, to prevent oxidation of the material due to heating,
It is also effective to coat the surface of a film or coating layer formed on the substrate.

The foil or thin wire is preferably formed by a molten metal quenching method, and preferably has a thickness or diameter of 0.1+m or less.

In particular, in order to produce foil or thin wire with a crystal grain size of 0.1 μm or less, a thickness or diameter of 0.05 m or less is preferable.

The powder is preferably formed by the Gaia atomization method in which molten metal is sprayed with a gaseous or liquid refrigerant and then poured into water for rapid cooling.The particle size is preferably 0.1 m or less, particularly ultrafine powder with a particle size of 1 μm or less. is preferred.

The film can be formed by vapor deposition, sputtering, CVD electroplating, chemical plating, etc., as described above.

In particular, sputtering is preferable to form a film with a thickness of 0.1 μl or less, and sputtering allows easy control of the target alloy composition.

It is also effective to divide the film to the same extent as the memory unit by chemical etching.

(Structure) The alloy of the present invention must have a different crystal structure at high and low temperatures, and must have a composition of a supercooled phase in which the crystal structure at high temperature is maintained at low temperature by rapid cooling from high temperature. It has a regular lattice crystal structure, but
For example, the supercooled phase is preferably an intermetallic compound having a Cs-CD type or DO1 type regular lattice, and the alloy of the present invention is an alloy that mainly forms this intermetallic compound as it can greatly change the optical properties. is preferred, especially a composition in which the entire alloy forms an intermetallic compound; this intermetallic compound is called an electronic compound.

In particular, alloy compositions near 3/2 electron compounds (average outer shell electron concentration e/a of 3/2) are good.

Further, the alloy of the present invention preferably has an alloy composition having solid phase transformation, and the alloy can be obtained with a large difference in spectral reflectance by quenching from a high temperature and non-quenching.

The alloy of the present invention preferably has ultrafine crystal grains, and the crystal grain size is particularly preferably 0.1 μm or less.

That is, the crystal grains are preferably smaller than the wavelength of visible light, but may be smaller than the wavelength of semiconductor laser light.

(Characteristics) The variable spectral reflectance alloy and recording material of the present invention can form at least two types of spectral reflectance in the visible light region at the same temperature. That is, it is necessary that the spectral reflectance of a material having a crystal structure (structure) formed by rapid cooling from a high temperature is different from that of a material having a crystal structure (structure) formed by non-quenching.

In addition, the difference in spectral reflectance obtained by quenching and non-quenching is preferably 5% or more, particularly preferably 10% or more.0 If the difference in spectral reflectance is large, it is easy to visually identify the color, It has remarkable effects in various applications described later.

As a light source for spectrally reflecting, electromagnetic waves other than visible light can be used, and infrared rays, ultraviolet rays, etc. can also be used.

Other properties of the alloy of the present invention include electrical resistivity, optical refractive index, optical polarization rate, optical transmittance, etc., which can be changed reversibly in the same way as spectral reflectance.
It can be used as a regeneration and detection means for sensors, etc.

Since the spectral reflectance is related to the surface roughness of the alloy, it is preferable that at least the intended portion has a mirror surface so as to have 10% or more in the visible light region as described above.

(Applications) The alloy of the present invention can be heated and rapidly cooled to partially or entirely change its physical or electrical properties such as spectral reflectance of electromagnetic waves, electrical resistivity, refractive index, polarization index, and transmittance due to a change in crystal structure. By utilizing changes in these characteristics, it can be used for elements such as recording, display, and sensors.

Electric energy in the form of voltage and current, electromagnetic waves (visible light, radiant heat) are used as a means of recording information, etc.

Infrared rays, violet rays, photographic flash lamp light, electron beams,
Proton beams, laser beams such as argon lasers, semiconductor lasers, heat, etc.) can be used, and it is particularly preferable to utilize changes in spectral reflectance due to irradiation as a recording medium for optical disks. There are digital audio discs (CAD or compact discs), video discs, memory discs, displays, etc., and by using the alloy of the present invention in the recording medium of optical discs, playback-only type, additional recording type, etc. It can be used in any rewritable disk device, and is particularly effective in rewritable disk devices.

An example of the principle of recording and reproduction when the alloy of the present invention is used in a recording medium of an optical disk is as follows.

First, the recording medium is locally heated and then rapidly cooled to maintain the crystal structure in the high temperature region in the low temperature region to record predetermined information, or the recording medium is locally heated using the high temperature phase as a pace. recorded locally by a low temperature phase during the high temperature phase,
Information can be reproduced by irradiating the recorded portion with light and detecting the difference in optical characteristics between the heated portion and the non-heated portion. Furthermore, the recorded information can be erased by heating the portion recorded as information at a temperature lower or higher than the heating temperature at the time of recording. The light is preferably a laser beam, and a short wavelength laser is particularly preferable. Since the reflectance of the heated portion and non-heated portion of the present invention is greatest at a wavelength around 500 nm or 800 nm, a laser beam having such a wavelength may be used for reproduction. Preferably, the same laser source is used for recording and reproduction.

For erasing, it is preferable to irradiate another laser beam with a lower energy density than that for recording.

Furthermore, a disk using the alloy of the present invention as a recording medium has a great advantage in that it can be visually determined whether information is recorded or not.

As a display, it is possible to partially change the spectral reflectance of visible light, so it is possible to record characters, figures, symbols, etc. without using paint, and these displays can be visually identified. . Furthermore, this information can be erased, and in addition to being used repeatedly by recording and erasing, it is also possible to store it permanently. Examples of its applications include clock faces and accessories.

As a sensor, there is a temperature sensor that utilizes changes in spectral reflectance, especially in visible light. Approximate temperature detection can be made by holding a sensor using the alloy of the present invention, whose temperature at which it changes to a high temperature phase is known in advance, in the temperature range to be measured, and maintaining the appropriate cool phase by cooling it appropriately.

(ls manufacturing method) The present invention provides a first temperature higher than room temperature in a solid state and a first temperature higher than room temperature in a solid state.
A part of the surface of the alloy having the chemical composition described above, which has a crystal structure different from that at the second temperature lower than the temperature, is rapidly cooled from the first temperature to form a crystal structure different from the crystal structure at the second temperature. and forming a region having a crystal structure formed by the rapid cooling and forming a different spectral reflectance between the region having the crystal structure formed by the rapid cooling and the region having the crystal structure at the second temperature. It is in the manufacturing method of the alloy.

Furthermore, the present invention provides a method for applying the first temperature to the entire surface of the alloy having the chemical composition described above, which has a different crystal structure at a first temperature higher than room temperature and a second temperature lower than the first temperature in a solid state. to form a crystal structure different from the crystal structure at the second temperature, and then heat a portion of the alloy surface to the second temperature to form a region having the crystal structure at the second temperature. and forming different spectral reflectances in the region having the crystal structure formed by the rapid cooling and the region having the crystal structure at the second temperature. be.

The cooling rate from the first temperature is 10”°C/second or more.

More preferably, it is 101° C./second or higher.

[Embodiments of the invention]

(Example 1) M g g T le in Ag-40wt%Zn alloy
An alloy containing only Ve(::r, Fe, AQg Snt Y) was melted in a vacuum high-frequency induction furnace to form an ingot. This ingot was golden in color. This ingot was melted and the molten metal was rotated at high speed. A ribbon-shaped foil was produced by pouring and rapidly cooling the metal on the surface of a single roll or between the rolls of a multi-roll.
The surface is Cr plated), the latter is Cu-Bs with a diameter of 120 mm.
It is made of rolls.

The roll was set at a circumferential speed of 10-20 m/s. A quartz nozzle was used to melt the master alloy, and approximately 10 g per charge was melted and rapidly cooled to produce a ribbon wiping material with a width of 5 m, a thickness of 40 pm, and a length of several meters. The color of this ribbon at room temperature was pink. When a portion of this product was heated at 180° C. for 1 minute, it showed a silvery white color at room temperature. Spectral reflectance was measured for these color tones.

Approximately 15% in pink and silvery white areas where the spectral reflectance is high
There was a difference between 6 and 0. Therefore, it is possible to distinguish between the two colors.

All of these colors can be stored permanently at room temperature. Furthermore, this shows that it is possible to store information such as signals, characters, symbols, etc. in pink on the silver-white base by local heating with a laser. Furthermore, it is possible to record information such as signals using silver-white on the opposite pink base.

(Example 2) A reversible change in color tone was confirmed in a thin film produced by sputter deposition. Diameter L from the ingot produced in Example 1
A disk with a thickness of 5IIll was cut out and used as a target for a sputtering device. A glass plate (thickness: 0.8 inch) was used as the sputter deposition substrate. A DC-magnetron was used to evaporate the 0 alloy film, in which a protective film (30 nm thick) of Sio was formed on the surface of the sputtered film to prevent thermal oxidation and peeling from the substrate during writing and erasing. An RF type sputtering method was used for the mold and the SiO□ film, respectively. The sputtering output was set to 140 to 200 W, and the substrate temperature was set to room temperature. Inside the container is 10-'Tor.
After evacuation to about r, Ar gas is heated to 5 to 30 mTor.
A thin film was prepared by introducing r.The film thickness was Sin, and the film was 30n.
The crystal grains of the alloy films (film thickness 300 nm) produced under sputter deposition conditions of 0 or more were made with various thicknesses of 0.05 to LOpm, and the crystal grains were ultrafine. The particle size is ultra-fine, approximately 30 nm, and is suitable for recording, playback,
It is believed that the grains have no effect on erasure. The as-deposited alloy film was pink in color.

18 About alloy film produced by sputtering method
After heating at 0℃ for 1 minute, it turned silvery white.

Writing using heating and cooling by Ar laser.

The mAr laser used for erasing is a continuous wave laser.

The sample was placed on a manual moving stage, and the sample was moved to focus and scan the laser beam on the film surface. The part irradiated with the laser light turns pink, and the same goes for the dotted line part written like a diagonal line. The writing is the result of scanning with a 200 mW Ar laser beam with a spot diameter of 10 μm.The 0 alloy film is heat-treated to become silvery white for each substrate.First, the focus of the laser beam is slightly shifted from the film surface, and the laser As a result, the original pink color was erased and changed to a silvery white color.From the results of 0 or more, it was found that even in thin film alloys, it is possible to erase the color by changing the color tone. was confirmed. It has been confirmed that this write and '/I4 write can be repeated any number of times.

Add A to the as-prepared pink sample at room temperature.
Set the i-laser output to about 50mW.

In the aAt'Ar laser scanning section, the color changed to silvery white and could be distinguished from the pink color of the base, indicating that recording was possible.

Thereafter, when the whole was heated to 180° C. at 1 + sin, the pink portion changed to silvery white, and at room temperature the entire surface was silvery white, indicating that it was erasable.

(Example 3) The ingot produced in Example 1 was made into powder and its color change was examined. - After mechanically cutting the ingot, the chips were crushed. Since the ingot is brittle, it becomes a fairly fine powder in the form of chips, which was further crushed to about 1,100 mesh. When it was ground, it was silvery white, but when it was heated at 350°C for 1 minute and then cooled with water, it was confirmed that it turned pink.

Furthermore, the powder crushed from the ingot is made into powder with a particle size of several μm using a ball mill, mixed with organic matter, applied to a glass substrate, and fired in a non-oxidizing atmosphere to form an alloy film with a thickness of approximately 100 μm. did.

A SiO2 film with a thickness of about 30 nm was formed on the surface of this alloy film by vapor deposition. The glass substrate was mirror-polished, and after the alloy film was formed, it was mirror-polished in the same way. The alloy film as it is formed has a silvery white color, but it was confirmed that it changes to a pink color by irradiating it with laser light at a temperature at which it transforms into another phase, as described above.

〔Effect of the invention〕

According to the present invention, it is possible to reversibly change the color or spectral reflectance due to crystal-crystal phase transition, so f! can be used as an information recording medium. A remarkable effect can be obtained by recording and erasing data.

[Brief explanation of drawings]

FIG. 1 is an equilibrium phase diagram of the A g -Z n binary system, and FIG. 2 is a diagram showing the principle of recording and erasing by the heating and quenching process of the alloy of the present invention.

Claims (1)

[Claims] 1. Mainly composed of silver, 30 to 46% zinc by weight, and Ia, IIa, IVa, Va, VIa, VIIa, VIII of the periodic table,
A variable spectral reflectance alloy comprising an alloy containing a total of 15% or less of one or more of rare earth elements Ib to Vb. 2. A part of the alloy surface having a different crystal structure at a first temperature higher than room temperature and a second temperature lower than the first temperature in the solid state is formed by rapid cooling from the first temperature. having a crystal structure different from the crystal structure at the second temperature,
2. The variable spectral reflectance alloy according to claim 1, wherein the other alloy has a crystal structure at the second temperature and has a spectral reflectance different from that of the rapidly cooled crystal structure. 3. The variable spectral reflectance alloy according to claim 1 or 2, wherein the alloy contains an intermetallic compound. 4. The variable spectral reflectance alloy according to any one of claims 1 to 3, wherein the first temperature is higher than the solid phase transformation point. 5. A patent claim in which the difference between the spectral reflectance of a product having a crystal structure formed by the rapid cooling and the spectral reflectance of a product having a crystal structure at the low temperature formed by non-quenching is 5% or more. The variable spectral reflectance alloy according to any one of the ranges 1 to 4. 6. The spectral reflectance of the alloy is at a wavelength of 400 to 1000 nm.
10% or more of the variable spectral reflectance alloy according to any one of claims 1 to 5. 7. Claim 1, wherein the alloy is a non-bulk material.
The variable spectral reflectance alloy according to any one of items 1 to 6. 8. The variable spectral reflectance alloy according to any one of claims 1 to 7, wherein the alloy has a crystal grain size of 0.1 μm or less. 9. The variable spectral reflectance alloy according to any one of claims 1 to 8, wherein the alloy is any one of a thin film, foil, strip, powder, and thin wire. 10. Main component is silver, 30-46% zinc by weight and
I a, IIa, IVa, Va, VIa, VIIa, VIII, I b~
A recording material comprising an alloy containing a total of 15% or less of Vb and one or more rare earth elements. 11. An alloy having different crystal structures in a solid state at a first temperature higher than room temperature and a second temperature lower than the first temperature, wherein at least a part of the alloy surface is at the first temperature. 11. The recording material according to claim 10, having an alloy composition that forms a crystal structure different from the crystal structure at the second temperature when quenched from the recording material. 12. The recording material according to claim 10 or 11, which is a foil or thin wire formed by pouring the molten metal of the alloy onto the circumferential surface of a rotating roll made of a highly thermally conductive member. 13. Claim 10 or 11, which is a thin film formed by depositing the alloy by vapor deposition or sputtering.
Recording materials listed in section. 14. The recording material according to claim 10 or 11, which is a powder obtained by spraying the molten metal of the alloy using a liquid or gas cooling medium.